Optical disk units are known such as optomagnetic disk drivers, mini-disk players, laser disk players and the like, whereby an optical disk is used as a medium for recording and reproduction of video and/or audio signals. An optical pickup device is provided in such optical disk units for recording and reproducing data on the optical disk surface. A seeking operation is performed to position a laser beam from the optical pickup device relative to the optical disk surface, the seeking operation being controlled according to a difference between a current position and a target position of the laser beam.
A conventional head seek control apparatus shown in the block diagram of FIG. 1 includes a comparator 10 in which data is inputted signifying the current track position as a value which is one half of an actual value of the track position data; an adder/subtractor 20 for adding or subtracting the data from the comparator 10; a track-cross signal generator 30 responsive to a tracking error signal TE to generate a track-cross signal; a frequency/voltage convertor 40 for converting the frequency of the output from the track-cross signal generator 30 to a voltage value; a ROM 50 for outputting data stored at an address designated by the output from the adder/subtractor 20; a D/A convertor 60 for converting the digital signal from the ROM 50 to an analog form; a comparator/processor 70 for comparing the output signals from the frequency/voltage convertor 40 and the D/A convertor 60; an amplifier 80 for amplifying an output from the comparator/processor 70; and an actuator 90 having the amplified signal for displacement applied thereto. The velocity of displacement of the actuator 90 is detected by means of the voltage value of the tracking error signals TE applied through the frequency/voltage convertor 40. The error of the displacement velocity of the actuator 90 is detected as a value resulting from the comparison made by the comparator/processor 70 between the outputs from the frequency/voltage convertor 40 and the D/A convertor 60.
In this conventional head seek control apparatus, the continually varying velocity of the displacement of the head can not be detected as it is since the value must be latched before the subsequent clock is applied when the tracking error signal is converted to a voltage by the frequency/voltage convertor.